Fiber based product

ABSTRACT

The invention relates to a method for producing a fiber based product, wherein the method comprises the steps of: a) applying a binder composition over a at least one surface of at least one fiber based substrate; b) determining the distribution of the applied binder composition over the en-tire at least one surface of the at least one fiber based substrate; and c) based on the determination in step b) either accepting the treated at least one fiber based substrate for the production of the fiber based product or rejecting the treated at least one fiber based substrate from the production of the fiber based product. The invention further relates to a method for producing a binder composition, to a binder composition and to a fiber based product.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. § 371 National Phase Entry Applicationof International Application No. PCT/FI2015/050051 filed Jan. 27, 2015,which designated the U.S., and which claims priority to FI ApplicationNo. 20145090 filed Jan. 28, 2014, the contents of each of which areincorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The invention relates to a method for producing a fiber based product, amethod for producing a binder composition, a binder composition and afiber based product.

BACKGROUND OF THE INVENTION

Modern production processes in wood industry have a very high productionspeed. This brings about high requirements for the reliability andeffectiveness of quality control during the processes. It is well knownthat the traditional ways to monitor product defects during e.g. plywoodproduction result in high reject rates of the final product due to thedelay between the actual production and availability of quality testingresults thereof. For glued or impregnated products the main sources ofdefects are related to the binder and its interaction with thesubstrate. Already small differences between different glue batches(e.g. viscosity or molecular weight distribution) or in the propertiesof the substrate (e.g. moisture content or density) will significantlychange the adsorption and absorption behavior of the binder on and intothe substrate. Consequently, gluing phase is the most challenging partin plywood production process. Problems in gluing can usually be seenonly after hot pressing when it is already too late.

The inventors of the present invention have recognized a need for bettersystems to monitor the quality of the glued substrates on which bindercomposition has been applied. The current invention relates to a newmethod for producing a fiber based product, comprising a way to monitorthe uniformity of the applied binder composition.

PURPOSE OF THE INVENTION

The purpose of the invention is to provide a new type of method forproducing a fiber based product and to provide a method for producing abinder composition which allows for easy on-line monitoring of defectsimmediately after the gluing phase. The purpose of the invention is alsoto provide a new binder composition and a fiber based product.

SUMMARY

The method for producing a fiber based product according to the presentinvention is characterized by what is presented in claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawing, which is included to provide a furtherunderstanding of the invention and constitutes a part of thisspecification, illustrates embodiments of the invention and togetherwith the description helps to explain the principles of the invention.In the drawing:

FIG. 1 is a flow chart illustration of a method according to oneembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for producing a fiber basedproduct comprising the steps of:

a) applying a binder composition over at least one surface of at leastone fiber based substrate, which binder composition is prepared by usingat least polymerizable substance, crosslinking agent, and colorant, andwherein the colorant is used in an amount such that the differencebetween the color of the binder composition and the color of acorresponding binder composition prepared without the use of thecolorant, as measured on a Gardner scale, is at least 3 units;

b) determining the distribution of the applied binder composition overthe entire at least one surface of the at least one fiber basedsubstrate; and

c) based on the determination in step b) either accepting the treated atleast one fiber based substrate for the production of the fiber basedproduct or rejecting the treated at least one fiber based substrate fromthe production of the fiber based product.

The inventors of the present invention surprisingly found out thatadding a colorant into the binder composition in the amount according tothe present invention facilitates determination of the distribution ofthe binder composition applied on a surface of the fiber basedsubstrate. Especially, the inventors found out an efficient way toimmediately check the distribution before proceeding into otherproduction steps of fiber based product. This enhances the productionprocess, because if the binder composition is uniformly applied over thedesired surface of the fiber based substrate, the strength of the fiberbased product is good. Information on the distribution on the bindercomposition at the early stage of the production of the fiber basedproduct significantly reduces e.g. wood waste during the productionprocess.

The present invention further relates to a method for producing a bindercomposition comprising the step of preparing the binder composition byusing at least polymerizable substance, crosslinking agent, andcolorant, wherein the colorant is used in an amount such that thedifference between the color of the binder composition and the color ofa corresponding binder composition prepared without the use of thecolorant, as measured on a Gardner scale, is at least 3 units.

The corresponding binder composition is a reference binder composition.The corresponding binder composition is prepared in the correspondingway as the binder composition according to the present invention, exceptthat the colorant is excluded. In case the preparation of the bindercomposition according to the present invention includes adding thecolorant into a previously produced composition comprising cross-linkingagent polymerized with polymerizable substance, the corresponding bindercomposition is prepared in the same way as the binder compositionaccording to the present invention, except that the colorant is notadded into the corresponding binder composition. In case the preparationof the binder composition according to the present invention includespolymerizing the polymerizable substance, the cross-linking agent andthe colorant, the colorant is replaced, in the preparation of thecorresponding binder composition, with the same amount of apolymerizable substance before the polymerization step.

The present invention further relates to a binder composition obtainableby the method according to the present invention.

The present invention further relates to a fiber based productcomprising at least one fiber based substrate having a bindercomposition applied over at least one surface of the at least one fiberbased substrate, which binder composition is prepared by using at leastpolymerizable substance, cross-linking agent, and colorant, wherein thecolorant is used in an amount such that the difference between the colorof the binder composition and the color of a corresponding bindercomposition prepared without the use of the colorant, as measured on aGardner scale, is at least 3 units.

In one embodiment of the present invention the polymerizable substanceis a compound selected from the class of phenols. In one embodiment ofthe present invention the polymerizable substance is selected from agroup consisting of phenol, cresol, resorcinol and combinations thereof.In one embodiment of the present invention the polymerizable substanceis phenol. In one embodiment of the present invention the polymerizablesubstance is selected from a group consisting of bio-basedhydroxyphenols and their derivatives.

In one embodiment of the present invention the crosslinking agent isselected from a group of aldehydes. In one embodiment of the presentinvention the group of aldehydes comprises an aldehyde, a derivative ofan aldehyde, an aldehyde forming compound and any combination thereof.In one embodiment of the present invention the derivative of an aldehydeis hexamethylenetetramine or trioxane. In one embodiment of the presentinvention the crosslinking agent is selected from a group consisting ofan aromatic aldehyde, glyoxal, furfuryl alcohol, caprolactam and glycolcompounds. The aromatic aldehyde can be furfuryl aldehyde. In oneembodiment of the present invention the crosslinking agent is analdehyde, and preferably formaldehyde, paraformaldehyde or a combinationthereof.

In one embodiment of the present invention at least one catalyst is usedfor the production of the binder composition. In one embodiment of thepresent invention the catalyst is a base. In one embodiment of thepresent invention the catalyst is an alkali or an alkali earthhydroxide. In one embodiment of the present invention the catalystcomprises a salt or a hydroxide of an alkali metal. In one embodiment ofthe present invention the catalyst is selected from a group consistingof sodium hydroxide, potassium hydroxide and any mixture thereof. In oneembodiment of the present invention the catalyst is an organic amine.

In one embodiment of the present invention, the at least one surface ofat least one fiber based substrate is any part of the total surface areaof the fiber based substrate. In one embodiment of the presentinvention, the at least one surface of at least one fiber basedsubstrate is half of the total surface area of the fiber basedsubstrate. In one embodiment of the present invention, the at least onesurface of at least one fiber based substrate means various shapes onthe surface of the fiber based substrate. In one embodiment of thepresent invention, the shape is a stripe or multiple stripes. In oneembodiment of the present invention, the shape is a spot or multiplespots. By “the entire at least one surface” of the at least one fiberbased substrate, it is meant the entire surface over which the bindercomposition has been applied. In other words, “the entire at least onesurface” is not necessarily the total surface area of the fiber basedsubstrate.

In one embodiment of the present invention the treated at least onefiber based substrate is, in step c), accepted for the production of thefiber based product when the applied binder composition is uniformlydistributed over the entire surface, as visually determined.

In one embodiment of the present invention the treated at least onefiber based substrate is, in step c), accepted for the production of thefiber based product when the contrast value is 50% or less, wherein thecontrast value is determined as (D_(s)−D_(t))/D_(s)·100%, wherein D_(s)is the reflection density of the binder composition and D_(t) is thereflection density of the surface of the at least one fiber basedsubstrate having the binder composition applied thereon, as measured byreflection densitometry.

Reflection densitometry is the practice of characterizing the amount oflight absorption of materials by measuring reflectance and calculatingand reporting reflection density. Reflection density (D) is thelight-absorbing property of a material, expressed as the logarithm ofthe reciprocal of the reflectance factor (R). Higher reflection densityis an indication of more light absorbed. Reflection density iscalculated as follows: D=log₁₀(1/R)=−log₁₀(R). Reflection density of thefiber based substrate over which binder composition has been applied, ismeasured by using a reflection densitometer or spectrodensitometeraccording to ASTM standard test method for reflection density of printedmatter (D7305-08a (Reapproved 2013)). Over a restricted range, thereflection density readings from a densitometer are approximatelyproportional to the binder composition film thickness, i.e. theuniformity of the applied binder composition.

Reflection densitometry can be used to determine whether the appliedbinder composition film is uniform by measuring the reflection densityover a wide area. Multiple reflection density measurements are taken inspecified positions on the surface over which binder composition hasbeen applied in order to determine an average result. For example, fivemeasurements are taken, one in each corner 25 mm from the edge of thesurface over which the binder composition has been applied and one inthe middle of the surface. The mean of the five readings is calculated.The contrast between the fiber based substrate over which the bindercomposition has been applied and the binder composition is determined.The contrast value is a measure of the uniformity of the bindercomposition layer on the surface of the fiber based substrate. Acontrast value of 50% or less is acceptable.

In one embodiment of the present invention the colorant is used in anamount such that the difference between the color of the bindercomposition and the color of a corresponding binder composition preparedwithout the use of the colorant, as measured on a Gardner scale, ispreferably at least 5 units, more preferably at least 7 units, and evenmore preferably at least 10 units.

In one embodiment of the present invention the colorant is used in anamount such that the difference between the color of the bindercomposition and the color of a corresponding binder composition preparedwithout the use of the colorant, as measured on a Gardner scale, is 3-18units, preferably 10-18 units, and more preferably 14-17 units. Thedifference between the color of the binder composition and the color ofa corresponding binder composition could also be higher than 18 units,but the upper limit of the Gardner scale is 18 units.

In one embodiment of the present invention the fibers of the fiber basedsubstrate are synthetic or natural fibers. Synthetic fibers are madefrom synthesized polymers or small molecules. Natural fibers are madefrom plant, animal and mineral sources. In one embodiment of the presentinvention the fibers of the fiber based substrate are wood based naturalfibers.

In one embodiment of the present invention the fiber based substrate isa veneer. In one embodiment of the present invention the fiber basedsubstrate is wood or wood containing material. In one embodiment of thepresent invention the fiber based substrate is a cellulose based timberproduct. In one embodiment of the present invention the fiber basedsubstrate is a gluelam product.

In one embodiment of the present invention the binder composition isapplied over at least one surface of at least two veneers and the atleast two veneers are glued together with the binder composition. In oneembodiment of the present invention at least two veneers are gluedtogether with the binder composition under the influence of hotpressing.

In one embodiment of the present invention the veneer is made ofsoftwood. In one embodiment of the present invention the veneer is madeof hardwood.

In one embodiment of the present invention the veneer is selected from agroup consisting of pine veneer, poplar veneer, beech veneer, spruceveneer, and birch veneer. In one embodiment of the present invention theveneer is spruce veneer or pine veneer. In one embodiment of the presentinvention the veneer is birch veneer.

In one embodiment of the present invention step a) comprises applying80-250 g, and more preferably 100-200 g of binder composition per squaremeter of veneer. The amount of binder composition applied per squaremeter of veneer according to the present invention results in goodcontact between the binder composition and the veneer, which leads to agood strength and wood failure value of the fiber based product.

In one embodiment of the present invention the fiber based substrate isa wood chip, paper, cardboard, or cotton. Wood chip is a piece of woodformed by cutting or chipping large pieces of wood. The size of woodchips may vary.

In one embodiment of the present invention the fiber based substratecomprises organic fibers, inorganic fibers, plastic fibers, glassfibers, carbon fibers, or any combination thereof. In one embodiment ofthe present invention the fiber based substrate comprises or consists ofmineral wool. In one embodiment of the present invention the fiber basedsubstrate comprises or consists of rock wool. In one embodiment of thepresent invention the fiber based substrate comprises or consists ofrubber, polyamide, or polyester. In one embodiment of the presentinvention the fiber based substrate comprises or consists of vulcanizedfiber.

In one embodiment of the present invention the polymerizable substance,the crosslinking agent and the colorant are polymerized. In oneembodiment of the present invention the step of preparing the bindercomposition comprises the step of polymerizing the polymerizablesubstance, the crosslinking agent and the colorant. In one embodiment ofthe present invention the binder composition according to the presentinvention is prepared by forming an aqueous composition comprisingcolorant, polymerizable substance and crosslinking agent, and byallowing polymerization reactions to take place between these reactantcomponents under the influence of heating the composition. In oneembodiment of the present invention the binder composition according tothe present invention is prepared by mixing colorant with a previouslyproduced composition comprising crosslinking agent polymerized withpolymerizable substance.

In one embodiment of the present invention the aqueous compositioncomprising at least polymerizable substance and crosslinking agent isheated at a temperature of 30-95° C. for allowing polymerizationreactions to take place, until a binder composition with a viscosityvalue of 80-1200 cp is formed.

In one embodiment of the present invention the aqueous compositioncomprising at least polymerizable substance, crosslinking agent, andcolorant is heated at a temperature of 30-95° C. for allowingpolymerization reactions to take place, until a binder composition witha viscosity value of 80-1200 cp is formed.

In one embodiment of the present invention the colorant is a phenoliccompound, preferably a wood-based phenolic compound, and more preferablylignin or tannin. Wood-based phenolic compounds, especially lignins andtannins, have a similar chemical structure as the PF resin. Therefore, ahomogeneous dispersion of components is formed, in which at least partof the components are solubilized. The formation of a homogeneousdispersion minimizes phase separation of the components.

In this specification, unless otherwise stated, the expression “lignin”should be understood as lignin originating from any suitable ligninsource. The lignin may include essentially pure lignin. By theexpression “essentially pure lignin” should be understood as at least90% pure lignin, preferably at least 95% pure lignin. In one embodimentof the present invention the essentially pure lignin comprises at most10%, preferably at most 5%, of other components. Extractives andcarbohydrates such as hemicelluloses can be mentioned as examples ofsuch other components. In one embodiment of the present invention thelignin contains less than 10 weight-%, preferably less than 6 weight-%,and more preferably less than 4 weight-% of carbohydrates. The amount ofcarbohydrates present in lignin can be measured by high performanceanion exchange chromatography with pulsed amperometric detector(HPAE-PAD) in accordance with standard SCAN-CM 71.

In one embodiment of the present invention the ash percentage of ligninis less than 7.5 weight-%, preferably less than 5 weight-%, and morepreferably less than 3 weight-%. The ash content can be determined bycarbonifying and quickly burning a lignin sample so that alkali saltsare not melted before the organic matter has been burned (e.g. 20-200°C. for 30 minutes, after which temperature is adjusted to 200-600° C.for 1 h, and thereafter adjusting the temperature to 600-700° C. for 1hour), and finally the lignin sample is ignited at 700° C. for 1 h. Ashcontent of a lignin sample refers to the mass that remains of the sampleafter burning and ignition, and it is presented as percent of thesample's dry content.

In one embodiment of the present invention the lignin is selected from agroup consisting of kraft lignin, steam explosion lignin, biorefinerylignin, supercritical separation lignin, hydrolysis lignin, flashprecipitated lignin, biomass originating lignin, lignin from alkalinepulping process, lignin from soda process, lignin from organosolspulping and combinations thereof. In one embodiment of the presentinvention the lignin is wood based lignin. The lignin can originate fromsoftwood, hardwood, annual plants or from a combination thereof.

In one embodiment of the present invention the lignin is Kraft lignin.By “kraft lignin” is to be understood in this specification, unlessotherwise stated, lignin that originates from kraft black liquor. Blackliquor is an alkaline aqueous solution of lignin residues,hemicellulose, and inorganic chemicals used in a kraft pulping process.The black liquor from the pulping process comprises componentsoriginating from different softwood and hardwood species in variousproportions. Lignin can be separated from the black liquor by different,techniques including e.g. precipitation and filtration. Lignin usuallybegins precipitating at pH values below 11-12. Different pH values canbe used in order to precipitate lignin fractions with differentproperties. These lignin fractions differ from each other by molecularweight distribution, e.g. Mw and Mn, polydispersity, hemicellulose andextractive contents. The molar mass of lignin precipitated at a higherpH value is higher than the molar mass of lignin precipitated at a lowerpH value. Further, the molecular weight distribution of lignin fractionprecipitated at a lower pH value is wider than of lignin fractionprecipitated at a higher pH value. The precipitated lignin can bepurified from inorganic impurities, hemicellulose and wood extractivesusing acidic washing steps. Further purification can be achieved byfiltration.

In one embodiment of the present invention the lignin is flashprecipitated lignin. The term “flash precipitated lignin” should beunderstood in this specification as lignin that has been precipitatedfrom black liquor in a continuous process by decreasing the pH of ablack liquor flow, under the influence of an over pressure of 200-1000kPa, down to the precipitation level of lignin using a carbon dioxidebased acidifying agent, preferably carbon dioxide, and by suddenlyreleasing the pressure for precipitating lignin. The method forproducing flash precipitated lignin is disclosed in patent applicationFI 20106073. The residence time in the above method is under 300 s. Theflash precipitated lignin particles, having a particle diameter of lessthan 2 μm, form agglomerates, which can be separated from black liquorusing e.g. filtration. The advantage of the flash precipitated lignin isits higher reactivity compared to normal kraft lignin. The flashprecipitated lignin can be purified and/or activated if needed for thefurther processing.

In one embodiment of the present invention the lignin is separated frompure biomass. The separation process can begin with liquidizing thebiomass with strong alkali followed by a neutralization process. Afterthe alkali treatment the lignin can be precipitated in a similar manneras presented above. In one embodiment of the present invention theseparation of lignin from biomass comprises a step of enzyme treatment.The enzyme treatment modifies the lignin to be extracted from biomass.Lignin separated from pure biomass is sulphur-free.

In one embodiment of the present invention the lignin is steam explosionlignin. Steam explosion is a pulping and extraction technique that canbe applied to wood and other fibrous organic material.

By “biorefinery lignin” is to be understood in this specification,unless otherwise stated, lignin that can be recovered from a refiningfacility or process where biomass is converted into fuel, chemicals andother materials.

By “supercritical separation lignin” is to be understood in thisspecification, unless otherwise stated, lignin that can be recoveredfrom biomass using supercritical fluid separation or extractiontechnique. Supercritical conditions correspond to the temperature andpressure above the critical point for a given substance. Insupercritical conditions, distinct liquid and gas phases do not exist.Supercritical water or liquid extraction is a method of decomposing andconverting biomass into cellulosic sugar by employing water or liquidunder supercritical conditions. The water or liquid, acting as asolvent, extracts sugars from cellulose plant matter and lignin remainsas a solid particle.

In one embodiment of the present invention the lignin is hydrolysislignin. Hydrolysed lignin can be recovered from paper-pulp orwood-chemical processes.

In one embodiment of the present invention the lignin originates from anorganosols process. Organosolv is a pulping technique that uses anorganic solvent to solubilize lignin and hemicellulose.

In one embodiment of the present invention, the lignin is alkalatedlignin. In one embodiment of the present invention, alkalated lignin isprepared before the preparation of the binder composition according tothe present invention.

In one embodiment of the present invention alkalated lignin is preparedusing the following method, comprising the steps of:

i) forming, under heating at a temperature of 30-98° C., an aqueousdispersion comprising alkali and lignin, wherein the alkali comprises ahydroxide of an alkali metal; and

ii) heating the dispersion formed in step a) at a temperature of 50-95°C.

In one embodiment of the present invention the alkali is selected from agroup consisting of sodium hydroxide, potassium hydroxide and a mixturethereof. In one embodiment of the present invention the alkali is sodiumhydroxide. In one embodiment of the present invention the concentrationof alkali is 5-50 weight-%, and preferably 10-25 weight-% based on thetotal weight of the dispersion in step i). In one embodiment of thepresent invention the concentration of lignin in step i) is 10-50weight-%, preferably 20-50 weight-%, and more preferably 20-45 weight-%based on the total weight of the dispersion in step i). In oneembodiment of the present invention step i) is carried out preferably ata temperature of 30-80° C., and more preferably at a temperature of30-70° C. In one embodiment of the present invention step i) is carriedout preferably at a temperature of 71-94° C. In one embodiment of thepresent invention step ii) is carried out for 15 minutes-24 hours,preferably for no longer than 5 hours, and more preferably for 0.5-1.5hours.

Alkalated lignin has an increased reactivity as compared to untreatedlignin or so-called raw lignin. Without limiting the invention to anyspecific theory about why step i) and step ii) results in a morereactive lignin being formed, it is to be considered that these stepsresult in the macromolecular structure of lignin being opened wherebythe steric hindrances that usually disable reactive groups in ligninstructures are removed. These steps, or a so-called alkalation process,may also add charged groups to the lignin macromolecule. The advantageof using alkalated lignin e.g. for producing a binder composition isthat the compatibility and reaction behavior is much better than in anormal case, where non-treated lignin has been used in the cooking orpolymerizing stage.

In one embodiment of the present invention the tannin used originatesfrom any wood species. Tannin may originate from e.g. bark or heartwood.Quebracho tree, beech tree and wattle tree are presented as examples ofpossible sources of tannin.

In one embodiment of the present invention the tannin used originatesfrom softwood bark. In one embodiment of the present invention thetannin is separated from softwood bark of debarking units in sawmills orpulp mills. The separation process can be combined with an ethanolextraction process, a hot water extraction process, a hot steamextraction process or a water-ethanol extraction process of softwoodbark.

In one embodiment of the present invention the tannin is condensedtannin. Condensed tannin has a high dry content and is thereforesuitable to be used in the present invention. The dry matter content ofcondensed tannin may vary between 40-100% and is suitably between 60-90%and preferably between 70-80%. Tannin with such dry matter content caneasily be dispersed, whereby a good reactivity with the other reactantcomponents is achieved. The tannin may also be hydrolysable tannin.

In one embodiment of the present invention the colorant is lignin andthe lignin has a weight average molecular weight of 500-10000 g/mol, andpreferably of 2000-8000 g/mol.

In one embodiment of the present invention the colorant is lignin andthe polydispersity index of lignin is 1.5-15, preferably 2-13, and morepreferably 3-9. The polydispersity index range of 3-9 results in lessvariation in the preparation of the binder composition and thus makes iteasier to control the preparation of the binder composition.

In one embodiment of the present invention the colorant is tannin andthe tannin has a weight average molecular weight of 1000-4000 g/mol, andpreferably of 1300-3000 g/mol.

In one embodiment of the present invention the colorant is tannin andthe polydispersity index of tannin is 1-6, preferably 1.1-4, and morepreferably 1.5-3. The polydispersity index range of 1.5-3 results inless variation in the preparation of the binder composition and thusmakes it easier to control the preparation of the binder composition.

When lignin or tannin of the weight average molecular weight range andpolydispersity index range according to the present invention is used asa colorant, the binder composition partly penetrates into the veneer andpartly stays on the surface of the veneer. Thus, the strength of theplywood prepared from the veneer is good.

The molecular weight of the lignin or tannin can be determined by usinga high-performance size-exclusion chromatography.

In one embodiment of the present invention, the molecular weight of thelignin or tannin is determined by using a high-performancesize-exclusion chromatography in the following manner: Two parallelmeasurements are carried out. 0.1 M NaOH is used as an eluent.Calibration is done using Na-polystyrene sulfonate standards having amolecular weight of 1100-73900 g/mol. For quality control, standardquality kraft lignin and PSS molecular weight standard are used. Thecolumns used are PSS MCX precolumns, 1000 Å and 100 000 Å separationcolumns filled with sulfonated styrene-divinylbenzene copolymer matrix.Isocratic run program is used. The run time is 45 minutes. The injectionvolume is 50 μl. The flux is 0.5 ml per minute. The temperature is 25°C. As a result of the chromatography, number average molecular weight(Mn), weight average molecular weight (Mw), peak molecular weight (Mp)and polydispersity index (PDI) values can be reported.

The polydispersity index (PDI) can be determined by size-exclusionhigh-performance liquid chromatography (SEC-HPLC). The polydispersityindex (PDI) is a measure of the distribution of molecular mass in agiven polymer sample. The PDI is calculated as the weight averagemolecular weight divided by the number average molecular weight. PDIindicates the distribution of individual molecular masses in a batch ofpolymers. The higher the polydispersity index of colorant, the wider themolecular weight distribution range of the colorant.

In one embodiment of the present invention the colorant is flavone dye,iso-quinoline dye, polyene colorant, pyran colorant, chromene dye,naphthochinone dye, chinone dye, anthrachinone dye, chromene dye,benzophyrone dye, indigoid dye or indole colorant.

In one embodiment of the present invention the fiber based substrate isa wood board and the binder composition is at least partly absorbed intothe at least one surface of the at least one wood board.

In one embodiment of the present invention the applied bindercomposition is uniformly distributed over the entire at least onesurface of the at least one fiber based substrate, as visuallydetermined.

In one embodiment of the present invention the contrast value is 50% orless, and the contrast value is determined as (D_(s)−D_(t))/D·100%,wherein D_(s) is the reflection density of the binder composition andD_(t) is the reflection density of the surface of the at least one fiberbased substrate having the binder composition applied thereon, asmeasured by reflection densitometry.

In one embodiment of the present invention the fiber based product isplywood and the average wood failure of the plywood is above 60%,preferably above 70%, and more preferably above 80%. Wood failure is ameasure of the strength of the binder composition. Wood failure isdetermined in accordance with standard EN314-1.

In one embodiment of the present invention 80-250 g, and more preferably100-200 g of binder composition is applied per square meter of veneer.

In one embodiment of the present invention the fiber based substrate isa wood chip.

In one embodiment of the fiber based product, the binder composition isobtained by the method according to the present invention.

The embodiments of the invention described hereinbefore may be used inany combination with each other. Several of the embodiments may becombined together to form a further embodiment of the invention.

The methods, the binder composition or the fiber based product, to whichthe invention is related, may comprise at least one of the embodimentsof the invention described hereinbefore.

An advantage of the method according to the present invention is thatthe method allows for a simple and fast determination of thedistribution of the binder composition over a surface of the fiber basedsubstrate during the production process of fiber based products. This isdue to the high contrast between the color of the binder composition andthe color of the fiber based substrate. Consequently, the methodenhances the overall production process of fiber based products. Thedistribution of the binder composition can be determined on-line, whichassists in detecting the gluing or impregnation defects. As a result,the amount of e.g. wood waste is reduced. The method also improves thequality of the final product, because the uniformity of the bindercomposition film applied on the fiber based substrate affects the finalproduct strength.

EXAMPLES

Reference will now be made in detail to the embodiments of the presentinvention, an example of which is illustrated in the accompanyingdrawing.

The description below discloses some embodiments of the invention insuch a detail that a person skilled in the art is able to utilize theinvention based on the disclosure. Not all steps of the embodiments arediscussed in detail, as many of the steps will be obvious for the personskilled in the art based on this specification.

FIG. 1 illustrates a method according to one embodiment of the presentinvention for producing a fiber based product.

Before applying the binder composition over at least one surface of atleast one fiber based substrate, the binder composition is prepared. Atleast polymerizable substance, crosslinking agent and colorant are usedfor the preparation of the binder composition. Also other components canbe used for the preparation of the binder composition. The colorant isused in such an amount that it results in at least 3 units differencebetween the color of the binder composition and the color of acorresponding reference binder composition. The reference bindercomposition is prepared under the same reaction conditions and using thesame component amounts as the binder composition according to thepresent invention, except that the colorant is excluded from thepreparation of the reference binder composition. The color of the bindercomposition and the reference binder composition are measured on aGardner scale.

The binder composition prepared as described above is then applied overat least one surface of at least one fiber based substrate. The bindercomposition may be applied over the total surface area of the fiberbased substrate. The binder composition may also be applied over certainareas on the surface of the fiber based substrate. Such areas may beshaped like stripes, spots, or any other shape.

After the application of the binder composition over the surface of thefiber based substrate, the distribution of the applied bindercomposition over the entire surface that was intended to be covered isdetermined. The determination can be done visually. The determinationcan also be done by determining the contrast value as described in thedescription above.

The treated fiber based substrate is then either accepted for theproduction of the fiber based product or rejected from the production ofthe fiber based product, based on the determination step describedabove.

Example 1 Preparing a Binder Composition

In this example a lignin phenol formaldehyde (LPF) binder compositionwas produced.

The following components and their amounts were used:

Concentration Mass Material (%) (g) NaOH 50 80 Water 145 Kraft lignin 73205 Formaldehyde 40 475 Phenol 90 300

In this example, and examples 2 and 7, the molecular weight distributionof lignin was determined by SEC-HPLC and the weight average molecularweight of the lignin used in these examples was 4000-6000 g/mol. Thepolydispersity index of the lignin used in these examples was determinedby SEC-HPLC and the polydispersity index of the lignin used in theseexamples was 4-6.

Firstly, a synthetic phenol formaldehyde (PF) binder composition wasproduced by polymerizing phenol and formaldehyde in the presence ofwater and sodium hydroxide (NaOH) as a catalyst. Formaldehyde was addedin a stepwise manner to an aqueous phenol composition and thereafter thetemperature of the formed composition was increased up to 80-90° C. Thecomposition was cooked at this temperature until a viscosity value of295 cP was reached. The viscosity was measured at 25° C. using a rotaryviscometer. To this composition, the lignin used as a colorant wasphysically mixed.

The lignin may also be alkalated lignin. Alkalated lignin can beprepared as described in Example 2.

The molecular weight distribution of the formed binder composition wasdetermined by SEC-HPLC. According to the results, the weight averagemolecular weight of the formed binder composition was 900-10000 g/mol.

The polydispersity index of the formed binder composition was determinedby SEC-HPLC. According to the results, the polydispersity index of theformed binder composition was 7.

The color difference of the binder composition formed as described aboveand the corresponding binder composition formed similarly except withoutthe addition of lignin, was determined on Gardner scale as described inExample 3. According to the results, the color difference was 10 units,as measured on Gardner scale.

The binder composition formed as above indicated was further used forthe production of fiber based product.

Example 2 Preparing a Binder Composition

In this example a LPF binder composition was produced.

The following components and their amounts were used:

Concentration Mass Material (%) (g) NaOH 50 103 Water 136 Kraft lignin73 145 Formaldehyde 37 268 Phenol 90 118

Firstly, alkalated lignin was prepared as follows. Water and part of thesodium hydroxide (65 g) were mixed and heating of the mixture wasstarted. Then lignin was dispersed slowly into the mixture of sodiumhydroxide and water with agitation and simultaneously the temperaturewas increased up to 60° C. When all of the lignin had been dispersed,the dispersion was heated at a temperature of about 76° C. for about 1hour.

Then the phenol was added in a stepwise manner to the above formedcomposition containing alkalated lignin, followed by the addition of thefirst part of the formaldehyde (125 g) also in a stepwise manner. Theformed composition was then cooked at a temperature of 70-80° C. forallowing the reactant components therein to react with each other.During this step of cooking the composition, the second part of theformaldehyde (143 g) was added to the composition. After addingformaldehyde into the composition, the composition was cooked for tenmore minutes, after which the last part of catalyst, NaOH (38 g), wasadded to the composition. Again, the composition was allowed to cook ata temperature of about 80-90° C. for about 2 hours and 47 minutes, afterwhich the process was ended by cooling down the reaction composition.

The molecular weight distribution of the formed binder composition wasdetermined by SEC-HPLC. According to the results, the weight averagemolecular weight of the formed binder composition was 11000-12000 g/mol.

The polydispersity index of the formed binder composition was determinedby SEC-HPLC. According to the results, the polydispersity index of theformed binder composition was 8.

The color difference of the binder composition formed as described aboveand the corresponding binder composition formed similarly except withoutthe addition of alkalated lignin, was determined on Gardner scale asdescribed in Example 3. In the corresponding binder composition,alkalated lignin was replaced with the same amount of phenol before thepolymerization step. According to the results, the color difference was17 units, as measured on Gardner scale.

The binder composition formed as above indicated was further used forthe production of fiber based product.

Example 3 Coloring of PF Binder Composition with Lignin and the Analysisof Color Change on Gardner Scale

The aim of this test was to create a method to evaluate the color of areference binder composition (phenol formaldehyde binder composition, PFbinder composition) and in addition to evaluate the color change in thebinder composition induced by the addition of lignin or alkalated lignin(lignin phenol formaldehyde binder composition, LPF binder composition).

The LPF binder composition (sample 8) was prepared as described inExample 2. The PF binder composition (sample 0, reference) was preparedin a corresponding manner except that alkalated lignin was replaced withthe same amount of phenol before the polymerization step.

The binder compositions were diluted with water to a concentration of 1g (dry mass of binder composition)/l. Diluted binder composition wasplaced in a test tube and the color of the dilution was visuallydetermined by comparing the color of the dilution with the color ofGardner laboratories reference samples.

Alkalated lignin or non-alkalated lignin (dry lignin) were then added todiluted PF binder composition according to table 2 in a concentration of10 g/l. The lignin content of alkalated lignin was 30%. The samples andtheir description are presented in table 1.

The solution was then also diluted to a concentration of 1 g/l. Thecolor of the solution was visually determined by comparing the color ofthe solution with the color of Gardner laboratories reference samples.The color of the binder composition with or without lignin addition ispresented in table 2.

TABLE 1 Samples and their description Sample Description 0 Reference 1Alkalated 1 2 Alkalated 2 3 Alkalated 3 4 Alkalated 4 5 Alkalated 5 6Dry lignin 1 7 Dry lignin 2 8 Lignin polymerized to PF bindercomposition

TABLE 2 Lignin and alkalated lignin amounts and the results of the colormeasurements Dry Phenol in Added Added Value binder diluted alkalateddry Lignin/ on Sam- composition sample lignin lignin Phenol Gardner ple(g) (g) (g) (g) (%) scale 0 1 0.5 0 0 0 <1 1 1 0.5 0.17 0 10 3 2 1 0.50.5 0 30 5 3 1 0.5 0.83 0 50 10 4 1 0.5 1.67 0 100 13 5 1 0.5 3.33 0 20018 6 1 0.5 0 0.1 20 3 7 1 0.5 0 0.15 30 6 8 1 0.5 0 0 50 18

According to the results, the addition of lignin changed the color ofthe diluted binder composition. The change was noted immediately afterthe addition of alkalated lignin and when dry lignin powder wasdispersed in binder composition. Further according to the results, theaddition of dry or alkalated lignin gave similar response on Gardnerscale. Samples 1 and 6 were not accepted for production of fiber basedproduct, because the difference of the color of the binder compositionand the color of the corresponding reference binder composition (sample0) was less than 3 units.

Example 4 Coloring of PF Binder Composition with Tannic Acid and theAnalysis of Color Change on Gardner Scale

The aim of this test was to evaluate the color change in bindercomposition induced by addition of tannic acid.

The PF binder composition was prepared as described in Example 1.

Binder composition was diluted with water to a concentration of 1 g (drymass of resin)/l. Diluted binder composition was placed in a test tubeand the color of the dilution was visually determined by comparing thecolor of the dilution with the color of Gardner laboratories referencesamples.

Tannic acid (CAS: 1401-55-4, C76 H52 O46), which is a specific type oftannin, was then added to diluted PF binder composition according totable 3. To 1 g of binder composition 0, 1, 2 or 4 g of tannic acid wasadded and the solution was mixed. The molecular weight distribution ofthe tannic acid was determined by SEC-HPLC and the weight averagemolecular weight of the tannic acid used was 1700 g/mol. Thepolydispersity index of the tannic acid used in this example wasdetermined by SEC-HPLC and the polydispersity index of the tannic acidused was 1.5.

The solution was then diluted to a concentration of 1 g/l. The color ofthe solution was visually determined by comparing the color of thesolution with the color of Gardner laboratories reference samples. Thecolor of the binder composition with or without tannic acid addition ispresented in table 3. The dry matter content (DMC) of the bindercomposition was determined by heating the sample at a temperature of 60°C. for 6 hours.

TABLE 3 Tannic acid amounts and the results of the color measurement DryBinder Diluted binder composi- binder Value composi- tion composi-Tannin/ Added on Sam- tion DMC tion Phenol tannin Gardner ple (g) (%)(g) (%) (g) scale 0 1 45.8 2.2 0 0 <1 1 1 45.8 2.2 200 1 3 2 1 45.8 2.2400 2 6 3 1 45.8 2.2 800 4 11

According to the results, the addition of tannic acid changed the colorof the diluted binder composition. The change was noted immediatelyafter the addition of tannic acid into the binder composition. Sample 1was not accepted for production of fiber based product, because thedifference of the color of the binder composition and the color of thecorresponding reference binder composition (sample 0) was less than 3units.

Example 5 Coloring of PF Binder Composition with Flavone Dye Quercitrinand the Analysis of Color Change on Gardner Scale

The aim of this test was to evaluate the color change in bindercomposition induced by the addition of flavone dye quercitrin.

The PF binder composition was prepared as described in Example 1.

Binder composition was diluted with water to a concentration of 1 g (drymass of resin)/l. Diluted binder composition was placed in a test tubeand the color of the dilution was visually determined by comparing thecolor of the dilution with the color of Gardner laboratories referencesamples.

Quercitrin dye (CAS: 522-12-3) was then added to diluted PF bindercomposition according to table 4. To 1 g of binder composition 0, 0.5, 1or 2 g of quercitrin dye was added and the solution was mixed.

The solution was then diluted to a concentration of 1 g/l. The color ofthe solution was visually determined by comparing the color of thesolution with the color of Gardner laboratories reference samples. Thecolor of the binder composition with or without quercitrin dye additionis presented in table 4.

TABLE 4 Quercitrin dye amounts and the results of the color measurementBinder Diluted Added Value Dry binder composition binder quercitrin oncomposition DMC composition dye Gardner Sample (g) (%) (g) (g) scale 0 145.8 2.2 0 <1 1 1 45.8 2.2 0.5 3 2 1 45.8 2.2 1 5 3 1 45.8 2.2 2 8

According to the results, the addition of quercitrin dye significantlychanged the color of the diluted binder composition. The change wasnoted immediately after the addition of quercitrin dye into the bindercomposition. Sample 1 was not accepted for production of fiber basedproduct, because the difference of the color of the binder compositionand the color of the corresponding reference binder composition (sample0) was less than 3 units.

Instead of quercitrin dye, any other colorant, such as iso-quinolinedye, polyene colorant, pyran colorant, chromene dye, naphthochinone dye,chinone dye, anthrachinone dye, chromene dye, benzophyrone dye, indigoiddye or indole colorant, may similarly be used as the colorant.

Example 6 The Use of a Binder Composition for Producing Plywood

The binder composition of Example 1 or Example 2 was used in theproduction of plywood. Spruce veneer was used.

The binder composition was applied over the surface of at least one sideof the veneers. The distribution of the applied binder composition overthe surface of the veneer was determined as follows. The reflectiondensity (D_(t)) of the surface, on which the binder composition wasapplied, was measured by reflection densitometry according to ASTMstandard test method for reflection density of printed matter (D7305-08a(Reapproved 2013)). Five separate measurements were taken in each cornerand in the middle of the surface over which the binder composition hadbeen applied. The mean of the five measurements were calculated. Thereflection density of the binder composition (D_(s)) was also measuredby reflection densitometry. The contrast value was determined as(D_(s)−D_(t))/D·100%. The contrast value was 20% when the bindercomposition of Example 1 was used, and 15% when the binder compositionof Example 2 was used. The contrast value was found acceptable and thetreated veneers were accepted for the production of plywood.

The accepted veneers were used in plywood production in the followingmanner. The wood veneers were joined together by the binder compositionto form plywood. The wood veneers with the binder composition werepressed by hot-pressing technique. The plywood hot-pressing temperatureused was about 130° C. For determining the optimum hot-pressing timeneeded for the different plywood, the temperature rise of the innermostglue line of the plywood panel was followed. The hot-pressing time wasthe time it took to reach 100° C., plus two minutes for curing thebinder composition.

Example 7 Preparing a Binder Composition and Applying the BinderComposition on Rock Wool

First, a LPF binder composition was produced. The following componentsand their amounts were used.

Concentration Mass Material (%) (g) NaOH 50 110 Water 225 Lignin 70 170Formaldehyde 37 1090 Phenol 90 535 Urea 100 110 Borax 100 45 Boric acid100 25

Firstly, water, sodium hydroxide, phenol and lignin were mixed. Then,borax was added to the dispersion and the components were allowed toreact for one hour at 50° C. Formaldehyde was then added and thedispersion was heated at a temperature of 65° C. for 2.5 hours. Thedispersion was then allowed to cool to 40° C. and boric acid and ureawere added, respectively.

The lignin may also be alkalated lignin. Alkalated lignin can beprepared as described in Example 2.

The molecular weight distribution of the formed binder composition wasdetermined by SEC-HPLC. According to the results, the weight averagemolecular weight of the formed binder composition was 5000-6500 g/mol.

The polydispersity index of the formed binder composition was determinedby SEC-HPLC. According to the results, the polydispersity index of theformed binder composition was 7.5.

The color difference of the binder composition formed as described aboveand the corresponding binder composition formed similarly except withoutthe addition of lignin, was determined on Gardner scale as described inExample 3. In the corresponding binder composition, lignin was replacedwith the same amount of phenol before the polymerization step. Accordingto the results, the color difference was 16 units, as measured onGardner scale.

The binder composition formed as above indicated was then applied onrock wool as follows. Mixture of volcanic stones and coke were fed to afurnace. The melt was allowed to run out of the bottom of the furnaceonto the spinning machine, where fibers of rock wool were spun to giverock wool with a fiber-like structure. The spinning was continued whileminor amounts of binder composition prepared as above and oil weresprayed on the individual fibers of rock wool, i.e. the fiber basedsubstrate, in order to apply the binder composition on rock wool. Therock wool fibers, on which the binder composition was applied, were thencollected on a belt conveyor.

The distribution of the applied binder composition over the entiresurface of the rock wool fibers was determined by visually detectingthat the surface of the fibers was colored. According to the visualdetermination the rock wool was accepted for the production of the fiberbased product, i.e. a cured rock wool mat.

Example 8 Applying a Binder Composition on Wood Chips

The binder composition of Example 1 or Example 2 was applied on woodchips.

The binder composition was applied over at least one surface of the woodchip. The distribution of the applied binder composition over the entiresurface of the wood chip was determined as described in Example 5.

The contrast value was 30% when the binder composition according toExample 1 was used and 15% when the binder composition according toExample 2 was used. The contrast value was found acceptable and thetreated wood chips were accepted for the production of fiber basedproduct.

It is obvious to a person skilled in the art that with the advancementof technology, the basic idea of the invention may be implemented invarious ways. The invention and its embodiments are thus not limited tothe examples described above; instead they may vary within the scope ofthe claims.

The invention claimed is:
 1. A method for producing a fiber basedproduct, the method comprising: a) applying a binder composition over atleast one surface of at least one fiber based substrate to provide atreated at least one fiber based substrate, wherein the fiber basedsubstrate is a veneer, a wood chip, paper, cardboard, or cotton, thebinder composition prepared by using at least a polymerizable substance,a crosslinking agent, and a colorant comprising lignin, wherein thecolorant is used in an amount such that the difference between a colorof the binder composition and a color of a corresponding bindercomposition prepared without the use of the colorant, as measured on aGardner scale, is at least 3 units; b) calculating the distribution ofthe applied binder composition over the entire at least one surface ofthe at least one fiber based substrate; and c) accepting the treated atleast one fiber based substrate for the production of the fiber basedproduct when contrast value is 50% or less, or rejecting the treated atleast one fiber based substrate from the production of the fiber basedproduct when the contrast value is greater than 50%, wherein thecontrast value is defined as (D_(s)-D_(t))/D_(s)*100%, wherein D_(s) isa reflection density of the binder composition, and D_(t) is areflection density of the surface of the treated at least one fiberbased substrate, as measured by reflection densitometry.
 2. The methodof claim 1, wherein the colorant is used in an amount such that thedifference between the color of the binder composition and the color ofa corresponding binder composition prepared without the use of thecolorant, as measured on a Gardner scale, is at least 5 units.
 3. Themethod of claim 1, wherein the polymerizable substance, thecross-linking agent and the colorant are polymerized.
 4. The method ofclaim 1, wherein the lignin has a weight average molecular weight of500-10000 g/mol.
 5. The method of claim 1, wherein the poly-dispersityindex of the lignin is 1.5-15.